function firstUniqChar(s: string): string {
    const map = new Map();
    for (let i = 0; i < s.length; i++){
        map.set(s[i], (map.get(s[i]) || 0) + 1);
    }

    for (let [k, v] of map.entries()) {
        if (v === 1) {
            return k
        }
    }
    return ''
};
